Photoresist strippers containing reducing agents to reduce metal corrosion

ABSTRACT

Alkaline photoresist stripping compositions containing reducing agent to reduce or inhibit metal corrosion. Reducing agents include compounds containing reactive multiple bonds, hydrazine and derivatives thereof, oximes, hydroquinone, pyrogallol, gallic acid and esters thereof, tocopherol, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid, BHT, BHA, 2,6-di-tert-butyl-4-hydroxymethyl-phenol, thiols, salicylaldehyde, 4-hydroxybenzaldehyde and glycol aldehyde dialkylacetals.

FIELD OF THE INVENTION

[0001] This invention relates to alkaline photoresist strippingcompositions containing reducing agents and the use of such strippingcompositions to reduce or inhibit metal corrosion and/or metal loss whenstripping photoresists from substrates containing metals such astungsten and/or copper and its alloys with aluminum.

BACKGROUND OF THE INVENTION

[0002] An integral part of microelectronic fabrication is the use ofphotoresists to transfer an image from a mask or reticle to the desiredsubstrate circuit layer. After the desired image transfer has beenachieved, the photoresist is removed, that is, stripped from thesubstrate before proceeding to some subsequent process step. Startingaround 1980, amides and mixtures of amides with various co-solvents haveroutinely been used for this stripping step, see for example Ward etal., U.S. Pat. No. 4,395,479; U.S. Pat. No. 4,428,871 and U.S. Pat. No.4,401,748.

[0003] Depending on the type of processing that is performed while thephotoresist is in place on the substrate, the photoresist polymer may becross-linked or hardened to the extent that amide-based solvents will nolonger effectively strip the photoresist. Starting around 1985, the useof amide mixtures containing additional alkaline components, such asorganic amines, (see Johnson U.S. Pat. No. 4,592,787; Merrem U.S. Pat.No. 4,765,844; Sizensky U.S. Pat. No. 4,617,251; Turner WO 87/05314 andThomas et al. U.S. Pat. No. 4,791,043) or quaternary ammonium hydroxides(see Steppan et al. U.S. Pat. No. 4,776,892; Haq U.S. Pat. No.4,744,834; Martin WO 88/05813) was introduced to facilitate the removalof such hardened photoresists.

[0004] The use of these alkaline components in strippers onmicrocircuits containing metals, particularly tungsten or copper and itsalloys with aluminum, can lead to metal loss. Various types of metalcorrosion, such as for example corrosion whiskers, pitting and notchingof metal lines, have been observed during the use of these alkalinestrippers. In the case of tungsten and copper corrosion can occur in theheated dry organic stripping composition mixtures with dissolved oxygenproviding the cathodic reaction.

[0005] It would therefore be most desirable to be able to providealkaline-containing photoresist stripping compositions suitable forstripping cross-linked or hardened photoresist polymer from substratescontaining metal in which metal corrosion and/or metal loss is reducedor inhibited. A further object of this invention is to provide a methodof stripping cross-linked or hardened photoresist from ametal-containing substrate using an alkaline-containing photoresiststripping composition containing an agent to reduce or inhibit suchmetal corrosion or metal loss.

BRIEF SUMMARY OF THE INVENTION

[0006] It has now been discovered that the inclusion of certain reducingagents in alkaline-containing photoresist stripping compositionsproduces photoresist stripping compositions that reduce or inhibit metalcorrosion and/or metal loss when such photoresist stripping compositionsare employed to remove cross-linked or hardened photoresist fromsubstrates containing metal. Reducing agents suitable for use inalkaline-containing photoresist stripping compositions of this inventionare the following: ascorbic acid, butyne diols, unsaturated ketones,uric acid, tetramisole, hydrazines and its derivatives includingcarbazates, oximes, hydroquinone, pyrogallol, gallic acid,2,4,5-trihydroxybutyrophenone, tocopherol,6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid,butylatedhydroxytoluene (BHT), butylatedhydroxyanisole (BHA),2,6-di-tert-butyl-4-hydroxymethylphenol, thiols, salicylaldehyde,4-hydroxybenzaldehyde and glycol aldehyde dialkyl acetals and mixturesthereof. The amount of reducing agent employed in the photoresiststripping compositions of this invention is any amount effective toreduce or inhibit metal corrosion or metal loss and will generally be anamount within the range of from about 0.1 to about 10% by weight basedupon the total weight of the photoresist stripping composition.

DETAILED DESCRIPTION OF THE INVENTION

[0007] The improved metal corrosion resistant photoresist strippingcompositions of this invention comprise an organic solvent system,alkaline components and at least one of the suitable reducing agents.The organic solvent system employed in the photoresist strippingcompositions of this invention is generally one having a solubilityparameter of from about 8 to about 15 obtained by taking the square rootof the sum of the squares of the three Hansen solubility parameters(dispersive, polar and hydrogen bonding). The solvent system maycomprise any of a number of individual solvents or a mixture of severaldifferent solvents. As examples of such solvents there may be mentioned,various pyrrolidinone compounds such as 2-pyrrolidinone,1-methyl-2-pyrrolidinone, 1-ethyl-2-pyrrolidinone,1-propyl-2-pyrrolidinone, 1-hydroxyethyl-2-pyrrolidinone,1-hydroxypropyl-2-pyrrolidinone, N-cyclohexylpyrrolidinone, and thelike, tri- or diethylene glycol monoalkyl ethers such as those of theformula HO(CH₂CH₂-O_(x)R where R is an alkyl radical of from 1 to 4carbon atoms and x is 2 or 3, compounds containing sulfur oxides such asdialkyl sulfones of the formula

[0008] where R¹ and R² are alkyl of 1 to 4 carbon atoms, dimethylsulfoxide (DMSO), tetrahydrothiophene-1,1-dioxide compounds of theformula

[0009] wherein R³ is hydrogen, methyl or ethyl, such as sulfolane,methyl sulfolane and ethyl sulfolane, as well as polyethylene glycols,dimethylacetamide or dimethylformamide. The solvent system portion ofthe stripper compositions of this invention will generally comprise fromabout 50% to about 98% by weight of the composition, preferably about70% to about 90% by weight.

[0010] Alkaline stripper components that may be used in this inventionalso cover a wide range of structural types. Their dissociationconstants, expressed as pRa values, range from about 9 to 11 for thebeta-oxygen or -nitrogen substituted amines to 8.3 for the secondaryamine, morpholine and hydroxylamines and hydroxylamine derivatives ofsomewhat lower pKa values. Among the alkaline components that may beused there may be mentioned, nucleophilic amines, preferably forexample, 1-amino-2-propanol, 1-amino-3-propanol,2-(2-aminoethoxy)ethanol, 2-aminoethanol, 2-(2-aminoethylamino)ethanol,2-(2-aminoethylamino)ethylamine, 1-(2-aminoethylpiperazine), and thelike. More important than the actual pKa value of an amine is itsnucleophilicity which should be high. The amount of amine componentemployed in the stripping compositions of this invention is from about1% to about 50%, preferably about 10% to about 30% by weight of thecomposition.

[0011] Reducing agents effective as oxygen scavengers useful as thereducing agents in the improved photoresist compositions of thisinvention are the following:

[0012] compounds containing reactive double bonds, that is, ascorbicacid, uric acid, butyne diols, unsaturated ketones such ascyclohexenylacetone and 3-nonene-2-one, and tetramisole;

[0013] hydrazine and its derivatives, that is, compounds of the formulaR⁴—NH—NH² where R⁴ is hydrogen or an organic radical, preferably ahydrogen, a formyl radical, an alkyl radical, an oxycarbonyl radical, ahydroxyalkyl radical, an alkylcarboxy radical or an aryl radical, forexample, a phenyl radical;

[0014] oximes;

[0015] readily oxidized aromatic compounds and oxidation inhibitors,that is, hydroquinone, pyrogallol, gallic acid and alkyl esters thereof,tocopherol, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid,butylatedhydroxytoluene, butylatedhydroxyanisole, and2,6-di-tert-butyl-4-hydroxymethylphenol;

[0016] thiols of the formula R⁵SH where R⁵ is an organic radical such asa heterocylic radical, carboxyaryl radical, a dicarboxyalkyl radical, anamino substituted carboxyalkyl radical or a radical of the formula

[0017] where R⁶ and R⁷ are alkyl radicals; and

[0018]  aldehydes and derivatives thereof, that is salicylaldehyde,4-hydroxybenzaldehyde and glycol aldehyde dialkyl acetals, particularlyglycol aldehyde diethyl acetal. Alkyl in the aforementioned reducingagents will generally be alkyl of 1 to about 12 carbon atoms, preferablyalkyl of 1 to 6 carbon atoms and more preferably alkyl of 1 to 4 carbonatoms.

[0019] Especially preferred as reducing agents for use in the strippingcompositions of this invention are ascorbic acid, uric acid,2-butyne-1,4-diol, 1-cyclohexenyl acetone, 3-nonene-2-one,2,3,5,6-tetrahydro-6-phenylimidazo[2,1-b] thiazole and the hydrochloridethereof, hydrazine, p-toluenesulfonylhydrazide, formic hydrazide, maleichydrazide, hydrazine hydrate, hydroxyethyl hydrazine, phenyl hydrazine,t-butyl carbazate, ethyl carbazate, salicylaldoxime, acetone oxime,pyrogallol, gallic acid, 2,4,5-trihydroxybutyrophenone,3,5-di-tert-butyl-4-hydroxytoluene, 3-tert-butyl-4-hydroxyanisole,2,6-di-tert-butyl-4-hydroxymethylphenol, tocopherol (Vitamin E),6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid, 2-mercapto-4[3H]quinazoline, dodecylmercaptopropionate, thiosalicylic acid,mercaptosuccinic acid, cysteine, 2-mercaptobenzoxazole, salicylaldehyde,4-hydroxybenzaldehyde and glycol aldehyde diethyl acetal.

[0020] The reducing agents of this invention will be employed in thealkaline-containing stripping compositions in an amount effective toreduce or inhibit metal corrosion or metal loss and will generally bewithin the range of from about 0.1 to about 10% by weight, preferablywithin from about 0.1 to about 5% by weight, more preferably within fromabout 0.1 to about 3% by weight and even more preferably within fromabout 1 to 3% by weight, based upon the total weight of the composition.

[0021] The stripping compositions of this invention are effective instripping a wide and varied range of photoresists especially positivephotoresists. Most photoresists consist of an ortho naphthoquinonediazide sulfonic acid ester or amide sensitizer or photoactivecomponent, with novolak, resole, polyacrylamide or acrylic copolymertype binders or resins. Such photoresists are well known in the art.Such resists and sensitizers are described for example, in U.S. Pat.Nos. 3,046,118; 3,046,121; 3,106,465; 3,201,239; 3,538,137; 3,666,473;3,934,057; 3,984,582 and 4,007,047. As examples of photoresistcompositions for which the stripping composition of this invention maybe used there may be mentioned: OCG Microelectronics Materials SeriesCAMP-6, HiPR 6500, HPR500, CG 825, CG 895, CG 897 and OiR 32photoresists; Hoechst Celanese Series AZ 1500, 6100, 6200B, 7500, 7500T,DX, P4000, and PF 500 photoresists; Shipley Company's Megaposit S1400,S1800, S3800, SPR2, SPR500-A, and SPRT500-A photoresists; MortonElectronic Materials' EL-, NOVA, and OFPR-series photoresists; TorayIndustries' EBR-9; and UCB-JSR Electronics' PFR-series photoresists.

[0022] The improved properties of stripping compositions of thisinvention are illustrated in the following example. In the example, thealkaline-containing solvent system stripping compositions to which areducing agent of this invention has been added are the followingcompositions A through O: Composition Components (Part by Weight) Adimethylformamide (90) + 2-aminoethanol (10) B dimethylacetamide (90) +2-aminoethanol (10) C dimethylacetamide (90) + 1-amino-3-propanol (10) Ddimethylacetamide (90) + 1-amino-2-propanol (10) E dimethylacetamide(60) + 1-amino-2-propanol (10) + sulfolane (30) F N-methylpyrro1idinone(60) + 1-amino-2-propanol (10) + N-cyclohexylpyrrolidinone (30) GN-methylpyrrolidinone (70) + 1-amino-2-propanol (30) HN-methylpyrrolidinone (90) + 2-(2-aminoethylamino) ethanol (10) Idimethyl sulfoxide (90) + 1-(2-aminoethylpiperazine) JN-methylpyrrolidinone (80) + 2-(2-aminoethylamino) ethanol (10) +N-(2-hydroxyethyl) pyrrolidinone (10) K N-methylpyrrolidinone (70) +2-(2-aminoethylamino) ethanol (10) + triethylene glycol monomethyl ether(20) L N-methylpyrrolidinone (60) + 2-(2-aminoethylamino) ethanol (10) +diethylene glycol monoethyl ether (30) M dimethyl sulfoxide (70) +1-amino-2-propanol (30) N N-methylpyrrolidinone (50) + 2-(2-aminoethoxy)ethanol (40) + sulfolane (10) O N-methylpyrrolidinone (60) +1-amino-2-propanol (10) + sulfolane (30).

[0023] The corrosion rates of the above alkaline-containing strippingcomposition were measured with and without added reducing agents of thisinvention and then the percent corrosion inhibition for the strippingcompositions of this invention were calculated. The corrosion rates weremeasured using the three following methods:

[0024] Method 1:

[0025] Coupons of 99.9+% tungsten (0.05×12×50 mm) were cleaned inacetone, dried, and weighed. Coupons were heated in one of the abovealkaline test compositions (plus 1% water to accentuate corrosion) withand without added reducing agents. After immersion in the testcompositions for 4 hours at 85° C., the coupons were removed, rinsedwith acetone, dried and reweighed. Weight losses were converted tocorrosion rates and finally to percent inhibition for the reducing agentused.

[0026] Method 2:

[0027] Identical to Method 1 except that the coupons were of 99.98%copper (0.025×12×50 mm).

[0028] Method 3:

[0029] Copper coupons (0.05×10×30 mm) were cleaned in isopropyl alcohol,dried then heated in 10 mL of stripping composition for one hour at 80°C. Copper uptake of the test solution was then measured using atomicabsorption spectroscopy and converted to percent inhibition for thereducing agent used.

[0030] Corrosion rates for stripping compositions A through O (without areducing agent of this invention) using methods 1, 2 and 3 are listedbelow in Angstroms per hour. Results were as follows: Angstrom/hr.Angstrom/hr. Composition Method Tungsten Copper A 1 38 B 1 120 C 1 58 D1 110 E 1 100 F 2 390 G 2 450 H 2 590 I 2 170 J 2 260 K 2 230 L 2 150 N2 730 N 3 430 O 3 860

[0031] Reducing agents of this invention were then included in theaforementioned stripping compositions and subjected to one of the threetest methods and corrosion loss measured. The percent inhibition ofcorrosion loss was then calculated according to the following equation:${{Percent}\quad {inhibition}} = {100\quad \left( {1 - \frac{{Corrosion}\quad {rate}\quad {with}\quad {reducing}\quad {agent}}{{Corrosion}\quad {rate}\quad {without}\quad {reducing}\quad {agent}}} \right)}$

EXAMPLE

[0032] Inclusion of reducing agents of this invention in theaforedescribed alkaline-containing stripping compositions A through Oproduced the following inhibition results. % Inhi- Stripping ReducingAgent bition of Test Method Composition (% by weight added) Metal Loss 1A ascorbic acid (1) 100 1 B 2-butyne-1,4-diol (2) 79 1 B uric acid (3)94 1 B 1-cyclohexenyl (5) 92 acetone 2 F ascorbic acid (2) 90 2 Hascorbic acid (2) 100 2 H 3-nonene-2-one (10) 93 2 I ascorbic acid (2)62 2 J ascorbic acid (2) 67 2 K ascorbic acid (2) 72 2 L ascorbic acid(2) 57 3 O ascorbic acid (.1) 91 3 O ascorbic acid (.5) 98 3 O ascorbicacid (1) 97 3 N ascorbic acid (.1) 92 3 N ascorbic acid (1) 92 3 O*Tetramisole (1) 91 hydrochloride 3 O *Tetramisole (1) 83 1 Bp-toluenesulfonyl (2) 75 hydrazide 1 A formic hydrazide (1) 100 1 Chydrazine (.5) 100 1 D hydrazine (.1) 64 1 D hydrazine (2) 87 1 B maleichydrazide (2) 62 3 O hydrazine hydrate (1) 99 3 O hydrazine hydrate (.1)98 3 O hydroxyethyl (1) 99 hydrazine 3 O phenyl hydrazine (1) 98 3 Otert-butyl (1) 97 carbazate 3 O formic hydrazide (1) 96 3 O ethylcarbazate (1) 97 3 O p-toluenesulfonyl (1) 98 hydrazide 3 N hydrazinehydrate (1) 96 1 B salicylaldoxime (5) 87 1 B acetone oxime (5) 78 1 Bhydroquinone (1) 100 1 E hydroquinone (1) 82 2 F pyrogallol (1) 63 2 Ggallic acid (3) 68 3 O hydroquinone (.1) 95 3 O hydroquinone (.5) 95 3 Ohydroquinone (1) 96 3 N hydroquinone (1) 87 1 B **BHT (3) 77 1 B VitaminE (1) 54 (tocopherol) 1 B ***Trolox (1) 72 1 C 2-mercapto-4[3H] (3) 86quinazoline 1 D dodecylmercapto- (5) 100 propionate 2 G thiosalicylicacid (3) 91 2 G mercaptosuccinic (3) 72 acid 2 M cysteine (3) 68 3 O2-mercapto-4[3H] (1) 86 quinazoline 3 O 2-mercapto-4[3H] (5) 89quinazoline 3 O 2-mercapto- (5) 95 benzoxazole 3 N 2-mercapto-4[3H] (1)88 quinazoline 1 D salicylaldehyde (5) 62 1 B glycol aldehyde (5) 81diethyl acetal 1 B 4-hydroxy- (5) 61 benzaldehyde

[0033] With the foregoing description of the invention, those skilled inthe art will appreciate that modifications may be made to the inventionwithout departing from the spirit thereof. Therefore, it is not intendedthat the scope of the invention be limited to the specific embodimentsillustrated and described.

1. An alkaline-containing photoresist stripping composition comprising astripping solvent, a nucleophilic amine and a reducing agent in anamount effective to inhibit or reduce metal corrosion when saidstripping composition is employed to strip hardened or cross-linkedphotoresist from a substrate containing metal, said reducing agent beingselected from the group consisting of a compound containing a reactivedouble bond, hydrazine and derivatives thereof, oximes, hydroquinone,pyrogallol, gallic acid, 2,4,5-trihydroxybutyrophenone,3,5-di-tert-butyl-4-hydroxytoluene, 3-tert-butyl-4-hydroxyanisole,tocopherol, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid,thiols, aldehydes and their derivatives.
 2. An alkaline-containingphotoresist stripping composition of claim 1 wherein the compoundcontaining a reactive double bond is selected from the group consistingof ascorbic acid, a butyne diol, an unsaturated ketone, uric acid andtetramisole; the hydrazine and derivatives thereof is selected fromthose of the formula R⁴—NH—NH² where R⁴ is hydrogen or an organicradical selected from a formyl, alkyl, oxycarbonyl, hydroxyalkyl,alkylcarboxy or aryl radical; the oxime is selected from the groupconsisting of salicylaldoxime and acetone oxime; the thiol is selectedfrom compounds of the formula R⁵SH where R⁵ is an organic radicalselected from the group consisting of heterocylic, carboxyaryl,dicarboxyalkyl, an amino substituted carboxyalkyl radical or a radicalof the formula

where R⁶ and R⁷ are alkyl radicals; and the aldehyde and derivativesthereof is selected from the group consisting of salicylaldehyde,4-hydroxybenzaldehyde and glycol aldehyde dialkyl acetal, and whereinalkyl in the above mentioned compounds is an alkyl radical of from 1 to12 carbon atoms.
 3. An alkaline-containing photoresist strippingcomposition according to claim 1 wherein the reducing agent is selectedfrom the group consisting of ascorbic acid, uric acid,2-butyne-1,4-diol, 1-cyclohexenyl acetone, 3-nonene-2-one,2,3,5,6-tetrahydro-6-phenylimidazo[2,1-b] thiazole and the hydrochloridethereof, hydrazine, p-toluenesulfonylhydrazide, formic hydrazide, maleichydrazide, hydrazine hydrate, hydroxyethyl hydrazine, phenyl hydrazine,t-butyl carbazate, ethyl carbazate, salicylaldoxime, acetone oxime,pyrogallol, gallic acid, 2,4,5-trihydroxybutyrophenone,3,5-di-tert-butyl-4-hydroxytoluene, 3-tert-butyl-4-hydroxyanisole,2,6-di-tert-butyl-4-hydroxymethylphenol, tocopherol,6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid,2-mercapto-4[3H]quinazoline, dodecylmercaptopropionate, thiosalicylicacid, mercaptosuccinic acid, cysteine, 2-mercaptobenzoxazole,salicylaldehyde, 4-hydroxybenzaldehyde and glycol aldehyde diethylacetal.
 4. An alkaline-containing photoresist stripping composition ofclaim 3 wherein the stripping solvent is a stripping solvent 'systemhaving a solubility parameter of from about 8 to about 15 and is presentin an amount of from about 50% to about 98% by weight of the strippingcomposition; the nucleophilic amine is present in an amount of fromabout 1% to about 50% by weight of the stripping composition; and thereducing agent is present in an amount of from about 0.1% to about 10%by weight of the stripping composition.
 5. An alkaline-containingphotoresist stripping composition of claim 4 wherein the strippingsolvent comprises one or more solvents selected from the groupconsisting of 2-pyrrolidinone, 1-methyl-2-pyrrolidinone,1-ethyl-2-pyrrolidinone, 1-propyl-2-pyrrolidinone,1-hydroxyethyl-2-pyrrolidinone, 1-hydroxypropyl-2-pyrrolidinone,N-cyclohexylpyrrolidinone, tri- or diethylene glycol monoalkyl ethers ofthe formula HO(CH₂CH₂—O_(x)R where R is an alkyl radical of from 1 to 4carbon atoms and x is 2 or 3, compounds containing sulfur oxidesselected from the group consisting of dialkyl sulfones of the formula

where R¹ and R² are alkyl of 1 to 4 carbon atoms, dimethyl sulfoxide,tetrahydrothiophene-1,1-dioxide compounds of the formula

wherein R³ is hydrogen, methyl or ethyl, sulfolane, methyl sulfolane andethyl sulfolane, polyethylene glycols, dimethylacetamide ordimethylformamide; and the amine is selected from the group consistingof nucleophilic amines, 1-amino-2-propanol, 1-amino-3-propanol,2-(2-aminoethoxy) ethanol, 2-aminoethanol, 2-(2-aminoethylamino)ethanol, 2-(2-aminoethylamino) ethylamine, and1-(2-aminoethylpiperazine).
 6. An alkaline-containing photoresiststripping composition of claim 4 wherein the solvent comprises1-methyl-2-pyrrolidinone, the amine comprises 1-amino-2-propanol or2-aminoethanol and the reducing agent comprises thiosalicylic acid. 7.In a method of stripping cross-linked or hardened photoresist resin froma metal containing substrate, the improvement comprising using thephotoresist stripping composition of claim 1 as the photoresiststripping composition.
 8. In a method of stripping cross-linked orhardened photoresist resin from a metal containing substrate, theimprovement comprising using the photoresist stripping composition ofclaim 2 as the photoresist stripping composition.
 9. In a method ofstripping cross-linked or hardened photoresist resin from a metalcontaining substrate, the improvement comprising using the photoresiststripping composition of claim 3 as the photoresist strippingcomposition.
 10. In a method of stripping cross-linked or hardenedphotoresist resin from a metal containing substrate, the improvementcomprising using the photoresist stripping composition of claim 4 as thephotoresist stripping composition.
 11. In a method of strippingcross-linked or hardened photoresist resin from a metal containingsubstrate, the improvement comprising using the photoresist strippingcomposition of claim 5 as the photoresist stripping composition.
 12. Ina method of stripping cross-linked or hardened photoresist resin from ametal containing substrate, the improvement comprising using thephotoresist stripping composition of claim 6 as the photoresiststripping composition.